Openwall GNU/*/Linux - a small security-enhanced Linux distro for servers
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Thu, 5 Oct 2017 12:11:32 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Thomas Garnier <thgarnie@...gle.com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>, "David S . Miller"
 <davem@...emloft.net>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar
 <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Peter Zijlstra
 <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Arnd Bergmann
 <arnd@...db.de>, Kees Cook <keescook@...omium.org>, Matthias Kaehlcke
 <mka@...omium.org>, Tom Lendacky <thomas.lendacky@....com>, Andy Lutomirski
 <luto@...nel.org>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
 Borislav Petkov <bp@...e.de>, "Rafael J . Wysocki" <rjw@...ysocki.net>, Len
 Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>, Juergen Gross
 <jgross@...e.com>, Chris Wright <chrisw@...s-sol.org>, Alok Kataria
 <akataria@...are.com>, Rusty Russell <rusty@...tcorp.com.au>, Tejun Heo
 <tj@...nel.org>, Christoph Lameter <cl@...ux.com>, Boris Ostrovsky
 <boris.ostrovsky@...cle.com>, Alexey Dobriyan <adobriyan@...il.com>, Andrew
 Morton <akpm@...ux-foundation.org>, Paul Gortmaker
 <paul.gortmaker@...driver.com>, Chris Metcalf <cmetcalf@...lanox.com>,
 "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, Nicolas Pitre
 <nicolas.pitre@...aro.org>, Borislav Petkov <bp@...en8.de>, "Luis R .
 Rodriguez" <mcgrof@...nel.org>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, Christopher Li <sparse@...isli.org>, Jason
 Baron <jbaron@...mai.com>, Dou Liyang <douly.fnst@...fujitsu.com>, "Rafael
 J . Wysocki" <rafael.j.wysocki@...el.com>, Mika Westerberg
 <mika.westerberg@...ux.intel.com>, Lukas Wunner <lukas@...ner.de>, Masahiro
 Yamada <yamada.masahiro@...ionext.com>, Alexei Starovoitov
 <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Markus
 Trippelsdorf <markus@...ppelsdorf.de>, Paolo Bonzini <pbonzini@...hat.com>,
 Radim Krčmář <rkrcmar@...hat.com>, Joerg Roedel
 <joro@...tes.org>, Rik van Riel <riel@...hat.com>, David Howells
 <dhowells@...hat.com>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Waiman
 Long <longman@...hat.com>, Kyle Huey <me@...ehuey.com>, Andrey Ryabinin
 <aryabinin@...tuozzo.com>, Jonathan Corbet <corbet@....net>, Matthew Wilcox
 <mawilcox@...rosoft.com>, Michal Hocko <mhocko@...e.com>, Peter Foley
 <pefoley2@...oley.com>, Paul Bolle <pebolle@...cali.nl>, Jiri Kosina
 <jkosina@...e.cz>, Rob Landley <rob@...dley.net>, "H . J . Lu"
 <hjl.tools@...il.com>, Baoquan He <bhe@...hat.com>, "Jan H .
 Schönherr" <jschoenh@...zon.de>, Daniel Micay
 <danielmicay@...il.com>, "the arch/x86 maintainers" <x86@...nel.org>, Linux
 Crypto Mailing List <linux-crypto@...r.kernel.org>, LKML
 <linux-kernel@...r.kernel.org>, Linux PM list <linux-pm@...r.kernel.org>,
 virtualization@...ts.linux-foundation.org, xen-devel
 <xen-devel@...ts.xenproject.org>, linux-arch <linux-arch@...r.kernel.org>,
 Sparse Mailing-list <linux-sparse@...r.kernel.org>, kvm list
 <kvm@...r.kernel.org>, linux-doc@...r.kernel.org, Kernel Hardening
 <kernel-hardening@...ts.openwall.com>
Subject: Re: [RFC v3 20/27] x86/ftrace: Adapt function tracing for PIE
 support

On Thu, 5 Oct 2017 09:01:14 -0700
Thomas Garnier <thgarnie@...gle.com> wrote:

> On Thu, Oct 5, 2017 at 6:06 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> > On Wed,  4 Oct 2017 14:19:56 -0700
> > Thomas Garnier <thgarnie@...gle.com> wrote:
> >  
> >> When using -fPIE/PIC with function tracing, the compiler generates a
> >> call through the GOT (call *__fentry__@...PCREL). This instruction
> >> takes 6 bytes instead of 5 on the usual relative call.
> >>
> >> With this change, function tracing supports 6 bytes on traceable
> >> function and can still replace relative calls on the ftrace assembly
> >> functions.
> >>
> >> Position Independent Executable (PIE) support will allow to extended the
> >> KASLR randomization range below the -2G memory limit.  
> >
> > Question: This 6 bytes is only the initial call that gcc creates. When
> > function tracing is enabled, the calls are back to the normal call to
> > the ftrace trampoline?  
> 
> That is correct.
> 

Then I think a better idea is to simply nop them out at compile time,
and have the code that updates them to nops to know about it.

See scripts/recordmcount.c

Could we simply add a 5 byte nop followed by a 1 byte nop, and treat it
the same as if it didn't exist? This code can be a little complex, and
can cause really nasty side effects if things go wrong. I would like to
keep from adding more variables to the changes here.

-- Steve

Powered by blists - more mailing lists

Your e-mail address:

Powered by Openwall GNU/*/Linux - Powered by OpenVZ